Iron type golf club head

ABSTRACT

A head  2  includes a face surface  4,  a back surface  6,  and a sole surface  8.  The back surface  6  includes a top side region Rt and a sole side region Rs. The sole side region Rs includes a sole side inclination surface Sb 1  inclined to increase a face thickness toward a sole side, a plurality of back recessed parts Rb 1  formed on the sole side inclination surface Sb 1,  and a wall WL 1  formed between the back recessed parts Rb 1  adjacent to each other. A low specific gravity member X 1  having a specific gravity lower than the specific gravity of the face material is disposed on at least one of the back recessed parts Rb 1.  The head  2  has a loft angle of equal to or greater than 42°. The head  2  has a sweet spot height of equal to or greater than 19 mm.

The present application claims priority on Patent Application No. 2016-38279 filed in JAPAN on Feb. 29, 2016, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an iron type golf club head.

Description of the Related Art

Of iron type golf club heads, a head having a large loft angle is particularly used for the purpose of stopping a ball at an aiming point. Thus, an increase in a backspin rate has been required.

Japanese Patent Application Laid-Open No. 2006-149478 (US2006/0111202A1) discloses a head in which a height D from a sole surface to a center of gravity of the head is greater than the radius of a ball. This head is intended to increase a backspin rate by a gear effect.

Japanese Patent No. 5660984 discloses a wedge in which a back part has a first weight part provided on a leading edge side and a second weight part provided on a top edge side. The second weight part has a weight greater than that of the first weight part, and therefore the center of gravity of the head is positioned at the top edge side. This head is also intended to increase a backspin rate by a gear effect.

SUMMARY OF THE INVENTION

According to an aspect of the present disclosure, an iron type golf club head can enhance controllability in approach shots.

In one aspect, a head may include a face surface formed by a face material, a back surface, and a sole surface extending between the face surface and the back surface. The back surface may include a top side region and a sole side region positioned between the top side region and the sole surface. The sole side region may include a sole side inclination surface inclined to increase a face thickness toward a sole side, a plurality of back recessed parts formed on the sole side inclination surface, and a wall formed between the back recessed parts adjacent to each other. A low specific gravity member having a specific gravity lower than that of the face material may be disposed on at least one of the back recessed parts. The head may have a loft angle of equal to or greater than 42°. The head may have a sweet spot height of equal to or greater than 18.5 mm.

In another aspect, a high specific gravity member having a specific gravity higher than that of the face material may be disposed on the top side region.

In another aspect, the number of the back recessed parts may be equal to or greater than 5. The number of the walls may be equal to or greater than 4.

In another aspect, the low specific gravity member may not be disposed on at least one of the back recessed parts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a plan view of a golf club head according to a first embodiment;

FIG. 2 shows a side view of the head in FIG. 1 as viewed from a toe side;

FIG. 3 shows a perspective view of the head in FIG. 1 as viewed from a back side;

FIG. 4 shows a perspective view of the head in FIG. 1 as viewed from a back side;

FIG. 5 shows a cross-sectional view taken along line A-A in FIG. 4;

FIG. 6 shows across-sectional view taken along line B-B in FIG. 4;

FIG. 7 shows a cross-sectional view in which a low specific gravity member is removed from FIG. 5;

FIG. 8 shows an enlarged view of FIG. 6;

FIG. 9 shows a perspective view of a head according to a second embodiment as viewed from a back side;

FIG. 10 shows a perspective view of a head according to a third embodiment as viewed from a back side;

FIG. 11 shows a perspective view of a head according to a fourth embodiment as viewed from a back side;

FIG. 12 shows a perspective view of a head according to a fifth embodiment as viewed from a back side; and

FIG. 13 shows a perspective view of a head according to a sixth embodiment as viewed from a back side.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Some aspects will be described later in detail based on preferred embodiments with appropriate reference to the drawings.

Each head according to the above described conventional techniques is intended to enhance a gear effect by making a higher center of gravity of the head higher, and to increase a backspin rate by the gear effect. However, since a limited head weight is distributed to a sole part and a top blade part, a center portion of the face is made thin. When the center portion of the face is thin, this portion has a higher coefficient of restitution. For this reason, a ball hit by the portion having a high coefficient of restitution may have a greater initial speed than the hitter expected, and may have a greater flight distance than the hitter aimed. Because of this phenomenon, flight distances are varied notably in approach shots. As a result, controllability in approach shots is deteriorated. These problems can be solved by embodiments described later.

FIG. 1 is a plan view of a golf club head 2 according to a first embodiment. FIG. 2 is a side view of the head 2 as viewed from a toe side. FIG. 3 is a perspective view of the head 2 as viewed from obliquely behind. FIG. 4 is a perspective view of the head 2 as viewed from an angle different from that of FIG. 3. FIG. 5 is a cross-sectional view taken along line A-A in FIG. 4. FIG. 6 is a cross-sectional view taken along line B-B in FIG. 4. FIG. 7 is an enlarged cross-sectional view in which a low specific gravity member is removed from FIG. 5. FIG. 8 is an enlarged view of FIG. 6.

The following terms are defined in the present application.

[Reference State]

The term “reference state” means a state where a head is placed on a horizontal plane h with a prescribed lie angle and a prescribed real loft angle (see FIG. 2). In the reference state, a center axis line (shaft axis line) of a shaft hole of the head is disposed in a perpendicular plane VP1 (see FIGS. 1 and 2). The perpendicular plane VP1 is a plane perpendicular to the horizontal plane h. In the reference state, the face surface is inclined with respect to the perpendicular plane VP1 at a real loft angle. The prescribed lie angle and real loft angle are appeared in a product catalog, for example.

[Toe-Heel Direction]

In the head of the reference state, a direction of an intersection line between the perpendicular plane VP1 and the horizontal plane h is the toe-heel direction.

[Face-Back Direction]

A direction perpendicular to the toe-heel direction and parallel to the horizontal plane h is the face-back direction.

[Top-Sole Direction]

A direction perpendicular to the toe-heel direction and parallel to the face surface is the top-sole direction.

[Up-Down Direction]

A direction of a straight line perpendicular to the horizontal plane h is the up-down direction.

[Score Line Region]

A region in which score lines gv are provided is referred to as the score line region in the present application. Definition of the score line region is as follows. A straight line Lt shown by a two-dot chain line in FIG. 1 is a straight line connecting toe side ends of longest score lines gv1. A straight line Lh shown by a two-dot chain line in FIG. 1 is a straight line connecting heel side ends of the longest score lines gv1. Respective straight lines Lx shown in FIG. 1 are straight lines connecting heel side ends of non-longest lines gv2. The score line region means a region surrounded by a score line gv10 located on the most top side, a score line gv12 located on the most sole side, the straight line Lt, the straight line Lh, and the plurality of straight lines Lx. In FIG. 1, the score line region is shown by dashed line hatching.

[Face Center]

In the determination of a face center, a center position C1 of the longest score line gv1 in the toe-heel direction is determined (see FIG. 1). At the center position C1 in the toe-heel direction, a center position of the face surface 4 (plane surface portion) in the up-down direction is the face center.

[Face Material]

A material constituting a face surface 4 is referred to as a face material. When the whole head is integrally formed by a single material, the face material is the material of the head. If the face surface 4 is formed by two or more kinds of materials, the face material is defined as a material constituting a largest area in the face surface 4.

The golf club head 2 is an iron type golf club head. An iron type golf club head is also simply referred to as an iron head. The head 2 is for right-handed golf players.

The golf club head 2 is a so-called wedge. The wedge usually has a loft angle (real loft angle) of is 42° or greater but 70° or less. The present embodiment is particularly effective in an approach shot. In this respect, the loft angle (real loft angle) of the head 2 is preferably equal to or greater than 42°, more preferably equal to or greater than 43°, still more preferably equal to or greater than 45°, still more preferably equal to or greater than 48°, and yet still more preferably equal to or greater than 50°.

The whole of the head 2 is integrally formed. The head 2 may be constituted with two or more members, although it is different from the present embodiment. For example, the head 2 may be formed by a face plate and a head body. The head 2 can be manufactured by a known method such as forging, casting, or the like.

The material of the head 2 is not limited. The head 2 may be made of a metal, or may be made of a nonmetal. Examples of the metal include iron, stainless steel, maraging steel, pure titanium, and a titanium alloy. Examples of the iron include soft iron (low carbon steel having a carbon content of less than 0.3 wt %). Examples of the stainless steel include SUS431. In the present embodiment, the material of the head 2 is a metal (soft iron).

The head 2 includes a face surface 4, a back surface 6, a sole surface 8, a top blade 10, and a hosel 12. The hosel 12 has a shaft hole 14. The top blade 10 may not be present.

As already described, the face surface 4 is constituted with the face material. The face material is not limited. The face material may be a metal, or may be a nonmetal. Examples of the metal include iron, stainless steel, maraging steel, pure titanium, and a titanium alloy. Examples of the iron include soft iron (low carbon steel having a carbon content of less than 0.3 wt %). Examples of the stainless steel include SUS431. In the present embodiment, the face material is a metal (soft iron).

As shown in FIG. 1, the score lines gv are provided on the face surface 4. The score lines gv include longest lines gv1 having a longest length and non-longest lines gv2 shorter than the longest lines gv1. The face surface 4 is a plane surface except a portion in which the score lines gv are provided.

A formation method of the score lines gv 8 is not limited. Examples of the formation method of the score lines gv include forging, press processing, casting, and cut processing (carving). In the cut processing, the cut processing of the score lines gv is carried out by using a cutter. In the press processing, a score line metal mold which has projections corresponding to the shapes of the score lines gv is used. The score line metal mold is forced on the face to form the score lines gv. In respect of the accuracy of the cross-sectional shapes of the score lines gv, the cut processing is preferable. Preferably, an NC processing machine is used for the cut processing of the score lines gv. NC stands for Numerical Control.

The score line region is subjected to a treatment for adjusting a surface roughness. A typical example of this treatment is a shot-blasting treatment. Irregularities are provided by the treatment. The irregularities contribute to increase in backspin.

The back surface 6 is a surface opposite to the face surface 4. The back surface 6 is positioned between the sole surface 8 and the top blade 10.

As is clear from FIG. 6 and the line, a surface opposite to the face surface 4 can also include the sole surface 8. However, the back surface 6 defined in the present application means a portion in which the sole surface 8 is excluded.

The back surface 6 includes a top side region Rt and a sole side region Rs. The top side region Rt is positioned between the top blade 10 and the sole side region Rs. The sole side region is positioned on the sole side of the top side region. The sole side region Rs is positioned between the top side region Rt and the sole surface 8.

A double-pointed arrow Tf in FIG. 8 shows a face thickness. The face thickness Tf is measured along a direction perpendicular to the face surface 4. The face thickness Tf can be measured at each point on the face surface 4.

As shown in FIGS. 3 and 6, the back surface 6 includes a sole side inclination surface Sb1. The sole side inclination surface Sb1 is inclined so that the face thickness Tf is increased toward the sole side. In other words, the sole side inclination surface Sb1 is inclined to increase in distance from the face surface 4 toward the sole side. A boundary line k1 between the top side region Rt and the sole side region Rs is formed by a set of initial points of the sole side inclination surface Sb1 (see FIGS. 3 and 4).

A plurality of back recessed parts Rb1 are formed on the sole side inclination surface Sb1. As shown in FIGS. 3 and 4, six back recessed parts Rb1 are provided in the present embodiment.

The plurality of back recessed parts Rb1 are arranged in the toe-heel direction. As shown in FIG. 4, the back recessed parts Rb1 include a back recessed part Rbh positioned on a most heel side and a back recessed part Rbt positioned on a most toe side. Furthermore, the back recessed parts Rb1 include a back recessed part Rbm positioned between the back recessed part Rbh and the back recessed part Rbt. In the present embodiment, the number of the back recessed parts Rbm is 4. The back recessed part Rbh positioned on the most heel side is positioned on the heel side with respect to the face center. The back recessed part Rbt positioned on the most toe side is positioned on the toe side with respect to the face center.

As shown in FIG. 7, each back recessed part Rb1 forms a space between the face surface 4 and the sole surface 8. If the back recessed part Rb1 is shallow, the back recessed part Rb1 may not form a space between the face surface 4 and the sole surface 8. In the present embodiment, the back recessed part Rb1 is deep. Thus, the back recessed part Rb1 forms the space between the face surface 4 and the sole surface 8.

As shown in FIG. 7, an inner surface of the back recessed part Rb1 includes a recessed part front surface Rb2 opposed to the face surface 4. The recessed part front surface Rb2 is a surface opposite to the face surface 4. However, in the present application, the recessed part front surface Rb2 is distinguished from the back surface 6. That is, the recessed part front surface Rb2 is not included in the back surface 6.

In the present embodiment, the recessed part front surface Rb2 is a plane surface. The recessed part front surface Rb2 may be a curved surface. In the present embodiment, the recessed part front surface Rb2 is parallel to the face surface 4. The recessed part front surface Rb2 may be inclined with respect to the face surface 4.

As shown in FIGS. 3 and 4, a wall WL1 is formed between back recessed parts Rb1 adjacent to each other. In the present embodiment, the plurality of walls WL1 are formed. Two or more walls WL1 can be formed by forming three or more back recessed parts Rb1. In the present embodiment, five walls WL1 are formed. As a result of forming six back recessed parts Rbl, five walls WL1 are formed. Generally, if the number of back recessed parts Rb1 is N, [N-1] walls WL1 can be formed. For example, when the number of the back recessed parts Rb1 is 5 or greater, the number of the walls WL1 can be 4 or greater. The wall WL1 extends in a direction perpendicular to the face surface 4.

A low specific gravity member X1 is disposed on at least one of the back recessed parts Rb1. As shown in FIG. 5, the low specific gravity member X1 completely occupies the back recessed part Rb1. The low specific gravity member X1 may not completely occupy the back recessed part Rb1. The low specific gravity member X1 is brought into contact with the recessed part front surface Rb2.

A boundary between an inside and an outside of the back recessed part Rb1 is also referred to as a recessed part boundary surface. The recessed part boundary surface is a surface covering an opening of the back recessed part Rb1. When the back recessed part Rb1 is formed by the cutting process, an outer surface before the cutting process can be considered as the recessed part boundary surface. In the present embodiment, an outer surface of the low specific gravity member X1 is formed to coincide with the recessed part boundary surface.

In the present embodiment, the low specific gravity member X1 is disposed on one of the plurality of back recessed parts Rb1. As shown in FIGS. 3 and 4, the low specific gravity member X1 is disposed on the third back recessed part Rb1 from the heel side. The low specific gravity member X1 is disposed on one of the back recessed parts Rbm. On the other hand, the low specific gravity member X1 is not disposed on the other five back recessed parts Rb1. That is, insides of these back recessed parts Rb1 are hollow. Thus, the low specific gravity member X1 is disposed on at least one of the plurality of back recessed parts Rb1, and the low specific gravity member X1 is not disposed on at least one of the back recessed parts Rb1.

The low specific gravity member X1 has a specific gravity lower than that of the face material. Therefore, the weight of the low specific gravity member X1 is smaller than a weight removed by forming the back recessed part Rb1.

As shown in FIG. 6, the top side region Rt includes a top side inclination surface Sb2 inclined to increase the face thickness Tf toward the top side. A boundary line k2 between the top side inclination surface Sb2 and the sole side inclination surface Sb1 coincides with the boundary line k1. The face thickness Tf is the minimum at the boundary line k1 (boundary line k2). The top side inclination surface Sb2 contributes to distribution of the weight of the head to the top side. The top side inclination surface Sb2 contributes to increase in a sweet spot height HS.

As shown in FIG. 8, the head 2 has a sweet spot SS. The sweet spot SS is an intersection point of the face surface 4 and a perpendicular line going down to the face surface 4 from a center of gravity G of the head. The sweet spot SS is positioned in the score line region. The sweet spot SS is positioned on the top side with respect to the boundary line k1 (see FIGS. 3 and 6). The sweet spot SS is positioned on the top side with respect to the boundary line k2 (see FIGS. 3 and 6). The sweet spot SS is positioned on the top side with respect to a minimum face thickness region.

A double pointed arrow HS in FIG. 8 shows a sweet spot height. The sweet spot height HS is measured along the up-down direction.

When a ball placed on a lawn and not teed up is hit, the hit point tends to be relatively a lower side. When the sweet spot height HS is low, the hit point tends to be close to the sweet spot SS. In this case, when the hit point is close to the sweet spot SS, the initial speed of the ball tends to be faster than the hitter intended and the trajectory of the ball tends to be high. Therefore, the flight distance becomes greater than the hitter intended. Furthermore, when the sweet spot SS is low, the gear effect is decreased and the backspin can be reduced. In light of controllability, the sweet spot height HS is preferably equal to or greater than 18.5 mm, more preferably equal to or greater than 19.0 mm, still more preferably equal to or greater than 19.5 mm, and yet still more preferably equal to or greater than 20.0 mm. In view of a sole width, there is a limitation for increasing the sweet spot height HS. In this respect, the sweet spot height HS is preferably equal to or less than 23 mm, and more preferably equal to or less than 22 mm.

FIG. 9 is a perspective view of a head 20 according to a second embodiment as viewed from behind. Difference between the head 20 and the head 2 is only a position of the low specific gravity member X1. In the head 20, the low specific gravity member X1 is disposed on the back recessed part Rb1 positioned on the most heel side. In addition, the low specific gravity member X1 is also disposed on the second back recessed part Rb1 from the heel side. The low specific gravity member X1 is not disposed on the other four back recessed parts Rb1. The head 20 in which the low specific gravity members X1 are disposed on the heel side is suitable for a golf player whose hit point is apt to be at the heel side.

FIG. 10 is a perspective view of a head 30 according to a third embodiment as viewed from behind. The difference between the head 30 and the head 2 is only a position of the low specific gravity member X1. In the head 30, the low specific gravity member X1 is disposed on the back recessed part Rb1 positioned on the most toe side. In addition, the low specific gravity member X1 is also disposed on the second back recessed part Rb1 from the toe side. The low specific gravity member X1 is not disposed on the other four back recessed parts Rb1. The head 30 in which the low specific gravity members X1 are disposed on the toe side is suitable for a golf player whose hit point is apt to be at the toe side.

FIG. 11 is a perspective view of a head 40 according to a fourth embodiment as viewed from behind. The difference between the head 40 and the head 2 is only the position of the low specific gravitymember X1. In the head 40, the low specific gravity member X1 is disposed on the back recessed part Rb1 positioned on the most toe side. In addition, the low specific gravity member X1 is also disposed on the back recessed part Rb1 positioned on the most heel side. The low specific gravity member X1 is not disposed on the other four back recessed parts Rb1. The low specific gravity members X1 positioned on the toe side and the heel side contribute to increase in the moment of inertia of the head.

All of the head 2, the head 20, the head 30 and the head 40 satisfy the following (a) and (b).

(a) The low specific gravity member X1 having a specific gravity lower than that of the face material is disposed on at least one of the back recessed parts Rb1.

(b) The low specific gravity member X1 is not disposed on at least one of the back recessed parts Rb1. In the other words, at least one of the back recessed parts Rb1 has a hollow inside.

As understood from the first to fourth embodiments, the position of the low specific gravity member X1 can be selected by providing the back recessed part Rb1 on which the low specific member X1 is disposed and the back recessed part Rb1 on which the low specific gravity member X1 is not disposed. In this case, the position of the low specific gravity member X1 can be selected in accordance with the tendency of the hit points of a golf player.

FIG. 12 is a perspective view of a head 50 according to a fifth embodiment as viewed from behind. The difference between the head 50 and the head 2 is the existence or non-existence of a cover member CV1. In the head 50, the cover member CV1 is added to the head 2. In FIG. 12, the cover member CV1 is shown by hatching. The cover member CV1 preferably covers at least one of the back recessed parts Rb1. In the present embodiment, the cover member CV1 covers all of the back recessed parts Rb1. Because of the existence of the cover member CV1, the back recessed parts Rb1 are not visually recognized. The appearance of the head 50 can be improved by the cover member CV1. One example of the cover member CV1 is a plate made of a metal.

FIG. 13 is a perspective view of a head 60 according to a sixth embodiment as viewed from behind. The difference between the head 60 and the head 2 is the existence or non-existence of a high specific gravity member Y1. In the head 60, the high specific gravity member Y1 is added to the topside region Rt of the head 2. In FIG. 13, the high specific gravity member Y1 is shown by hatching. The high specific gravity member Y1 contributes to increase in the sweet spot height HS. Preferably, a center of gravity of the high specific gravity member Y1 is positioned on an upper side with respect to a center of gravity of the head 60. Preferably, the center of gravity of the high specific gravity member Y1 is positioned on a first portion H1 (described later). More preferably, the whole high specific gravity member Y1 is positioned in the first portion H1 (described later).

A virtual line (two-dot chain line) in FIG. 13 shows a high specific gravity member Y2. The high specific gravity member Y2 is provided on the hosel 12. The high specific gravity member Y2 is provided on an upper portion of the hosel 12. The high specific gravity member Y2 provided on the upper portion of the hosel 12 is effective in making the center of gravity G of the head higher. In light of making the center of gravity G of the head higher, a distance between the center of gravity of the high specific gravity member Y2 and an end surface of the hosel 12 is preferably equal to or less than 25 mm, more preferably equal to or less than 20 mm, and still more preferably equal to or less than 15 mm. In view of the fixation of the high specific gravity member Y2, the high specific gravity member Y2 is preferably positioned apart from the end surface of the hosel 12. In this respect, the distance between the center of gravity of the high specific gravity member Y2 and the end surface of the hosel 12 is preferably equal to or greater than 1 mm, and more preferably equal to or greater than 5 mm.

[Weight Re-Distribution Effect by Back Recessed Part Rb1]

Conventionally, the sweet spot height HS is increased by distributing weight of the center portion of the face to the top side. As a result, the center portion of the face becomes thin and a locally high rebound property is generated at the center portion. On the other hand, in the present embodiment, since the back recessed parts Rb1 are provided, weight to be distributed on the back recessed parts Rb1 can be disposed to the top side. For this reason, the sweet spot height HS can be increased while the center portion of the face is not made thin. Therefore, the high rebound property at the center portion of the face is suppressed and variation in flight distances because of differences of hit points is suppressed. As a result, controllability in approach shots is enhanced.

The recessed part front surface Rb2 is formed by providing the back recessed part Rb1. In a portion on which the recessed part front surface Rb2 is formed, the face is consequently made thin. However, since the wall WL1 is provided, flexural deformation of the face involved in the formation of the back recessed part Rb1 is suppressed. In other words, since the recessed part front surface Rb2 is supported by the wall WL1, the flexural deformation of the recessed part front surface Rb2 is suppressed. Thus, a high rebound property involved in the formation of the back recessed part Rb1 is suppressed.

Furthermore, the low specific gravity member X1 is provided on at least one of the back recessed parts Rb1. The low specific gravity member X1 also contributes to the suppression of the deflection of the face. The high rebound property involved in the formation of the back recessed part Rb1 is suppressed by the wall WL1 and the low specific gravity member X1. In addition, since the low specific gravity member X1 has a small specific gravity, the weight re-distribution effect is maintained.

[Total Volume VR of Back Recessed Parts Rb1]

In light of enhancing the weight re-distribution effect, a total volume VR of the back recessed parts Rb1 is preferably equal to or greater than 3500 mm³, more preferably equal to or greater than 4000 mm³, and still more preferably equal to or greater than 4500 mm³. Since there is a limitation for the volume of the head, the total volume VR is preferably equal to or less than 6000 mm³, more preferably equal to or less than 5500 mm³, and still more preferably equal to or less than 5000 mm³. The total volume VR is the sum of volumes of all the back recessed parts Rb1.

[Interval DW of Walls WL1]

A double-pointed arrow DW in FIG. 9 shows an interval between the walls WL1. The interval DW is measured along the toe-heel direction. In light of enhancing the effect of suppression of the high rebound property, the interval DW is preferably small. Although it is said that a particularly sensitive sense of distance is required for an approach shot of 40 yards or less, a contact portion between the ball and the face surface 4 has a diameter of approximately 12 mm in an approach shot of around 40 yards. In those respects, the interval DW is preferably equal to or less than 12 mm, and more preferably equal to or less than 10 mm. In light of the weight re-distribution effect, the interval DW is preferably equal to or greater than 4 mm, more preferably equal to or greater than 6 mm, and still more preferably equal to or greater than 8 mm.

[Number N of Back Recessed Parts Rb1]

In light of providing walls WL1 at a preferable interval while increasing the total volume VR, the number N of the back recessed parts Rb1 is preferably equal to or greater than 3, more preferably equal to or greater than 4, and still more preferably equal to or greater than 5. If the number N is excessively great, the number of the walls WL1 becomes excessively great and the weight re-distribution effect can be deteriorated. In this respect, the number N of the back recessed parts Rb1 is preferably equal to or less than 10, and more preferably equal to or less than 8.

[Thickness of Wall WL1]

In light of enhancing the weight re-distribution effect, the wall WL1 has a thickness of preferably equal to or less than 4 mm, and more preferably equal to or less than 3 mm. In light of enhancing the effect of suppressing the deflection of the face, the thickness of the wall WL1 is preferably equal to or greater than 1 mm, and more preferably equal to or greater than 1.5 mm. The thickness of the wall WL1 is measured along the toe-heel direction.

[Hosel Length]

In light of making the center of gravity G of the head higher and increasing the sweet spot height HS, a hosel length is preferably equal to or greater than 66 mm, more preferably equal to or greater than 68 mm, and still more preferably equal to or greater than 70 mm. In light of easiness of address, the hold length is preferably equal to or less than 90 mm, and more preferably equal to or less than 85 mm. The definition of the hosel length is as follows. In the head of the reference state, an intersection point of a shaft axis line and the horizontal plane h is determined. A distance between the intersection point and a central point of the end face of the hosel 12 is defined as the hosel length.

[Minimum Face Thickness Tmin]

In the present application, a minimum face thickness Tmin is defined. The minimum face thickness Tmin is a minimum value of the face thickness Tf in the score line region.

As already described, the locally high rebound property deteriorates controllability. In light of enhancing controllability in approach shots, the minimum face thickness Tmin is preferably equal to or greater than 3.5 mm, more preferably equal to or greater than 4.0 mm, and still more preferably equal to or greater than 4.5 mm. In light of creating an excess weight for attaining a higher center of gravity, the minimum face thickness Tmin is preferably equal to or less than 7 mm, and more preferably equal to or less than 6 mm.

[Area Ma of Minimum Face Thickness Region]

A region having a face thickness Tf of the minimum face thickness Tmin is also referred to as a minimum face thickness region. When the minimum face thickness region is enlarged, a coefficient of restitution in the region is increased. Thus, variation of flight distances depending on hit points is increased to deteriorate controllability in approach shots. In light of enhancing the controllability, the area Ma of the minimum face thickness region is preferably equal to or less than 1000 mm², more preferably equal to or less than 900 mm², and still more preferably equal to or less than 850 mm². The area Ma may be less than 10 mm².

An area in which portions belonging to presence regions of the recessed part front surfaces Rb2 are excluded from the area Ma is defined as an area M1. In light of enhancing controllability, the area M1 is preferably equal to or less than 100 mm², more preferably equal to or less than 20 mm², still more preferably equal to or less than 10 mm², and yet still more preferably less than 10 mm². The area M1 may be 0 mm².

[Area Mb of Thin Region having Face Thickness Tf of 5 mm or Less]

A region having a face thickness Tf of 5 mm or less is also referred to as a thin region. If the face thickness Tf is equal to or less than 5 mm, a ball initial speed tends to be significantly great even when the head speed is relatively small as in approach shots. In light of suppressing the locally high rebound property and enhancing controllability in approach shots, the area Mb of the thin region is preferably small. Specifically, the area Mb of the thin region is preferably equal to or less than 1350 mm², more preferably equal to or less than 1250 mm², and still more preferably equal to or less than 1200 mm². The area Mb of the thin region may be 0 mm². In view of making the center of gravity of the head higher, the weight of the face center region is preferably distributed to the top side. In this respect, the area Mb of the thin region may be greater than 0 mm², further may be equal to or greater than 500 mm², and furthermore, may be equal to or greater than 1000 mm².

[Face Thickness Tf1 in Presence Regions of Recessed Part Front Surfaces Rb2]

In light of enhancing the weight re-distribution effect, the face thickness Tf1 in the presence regions of the recessed part front surfaces Rb2 is preferably equal to or less than 7.0 mm, more preferably equal to or less than 6.5 mm, and still more preferably equal to or less than 6.0 mm. Even when the face thickness Tf1 is thin as such, high rebound property in the presence regions of the recessed part front surfaces Rb2 is suppressed by the existence of the walls WL1. In view of the strength of the face surface 4, the face thickness Tf1 is preferably equal to or greater than 3.5 mm, more preferably equal to or greater than 4.0 mm, and still more preferably equal to or greater than 4.5 mm.

[Weights Wt1, Wt2, Wt3 of Regions Divided into Three Equal Parts]

As shown in FIG. 2, a point positioned on the most top side in the face body is defined as a point Pt. A point positioned on the most sole side in the face body is defined as a point Ps. Planes dividing the distance between the point Pt and the point Ps into three equal parts are defined as PL1 and PL2 (see FIG. 2). Both planes PL1 and PL2 are perpendicular to the face surface 4, and parallel to the toe-heel direction. The plane PL1 is positioned on the top side with respect to the plane PL2. The head 2 is divided into a first portion H1, a second portion H2 and a third portion H3 by the planes PL1 and PL2. The first portion H1 is a portion positioned on the top side with respect to the plane PL1. The second portion is a portion positioned between the plane PL1 and the plane PL2. The third portion is a portion positioned on the sole side with respect to the plane PL2.

A weight of the first portion H1 (top side) is defined as Wt1. A weight of the second portion H2 (center) is defined as Wt2. A weight of the third portion H3 (sole side) is defined as Wt3.

In light of suppressing the locally high rebound property and enhancing controllability in approach shots, Wt2/Wt1 is preferably equal to or greater than 1.6, more preferably equal to or greater than 1.7, and still more preferably equal to or greater than 1.8. In light of making the center of gravity G of the head higher, Wt2/Wt1 is preferably equal to or less than 3.2, more preferably equal to or less than 2.9, still more preferably equal to or less than 2.7, and yet still more preferably equal to or less than 2.6.

In light of suppressing the locally high rebound property, enhancing controllability in approach shots, and furthermore, making the center of gravity G of the head higher, Wt2/Wt3 is preferably equal to or greater than 0.85, more preferably equal to or greater than 0.87, still more preferably equal to or greater than 0.90, and yet still more preferably equal to or greater than 0.93. In view of arranging the walls WL1 at an appropriate interval, it is not preferable that Wt3 is excessively small. In this respect, Wt2/Wt3 is preferably equal to or less than 1.04, more preferably equal to or less than 1.01, and still more preferably equal to or less than 0.98.

In light of suppressing the locally high rebound property, enhancing controllability in approach shots, and furthermore, making the center of gravity G of the head higher, Wt1/Wt3 is preferably equal to or greater than 0.35, more preferably equal to or greater than 0.41, still more preferably equal to or greater than 0.43, and yet still more preferably equal to or greater than 0.45. In view of arranging the walls WL1 at an appropriate interval, it is not preferable that Wt3 is excessively small. In this respect, Wt1/Wt3 is preferably equal to or less than 0.60, more preferably equal to or less than 0.58, and still more preferably equal to or less than 0.56.

[Contact Area Mc between Low Specific Gravity Member X1 and Recessed Part Front Surface Rb2]

Controllability in approach shots is enhanced by suppressing a locally high rebound property caused by deflection of the recessed part front surface Rb2. In this respect, the low specific gravity member X1 is preferably brought into contact with the recessed part front surface Rb2. The effect of the low specific gravity member X1 is exhibited in a larger portion of the face region by enlarging a contact area Mc between the low specific gravity member X1 and the recessed part front surface Rb2. In this respect, the contact area Mc is preferably equal to or greater than 1000 mm², more preferably equal to or greater than 2000 mm², and still more preferably equal to or greater than 2500 mm². In light of increasing the sweet spot height HS, it is not preferable that the volume of the low specific gravity member X1 is excessively great. In view of this point, the contact area Mc is preferably equal to or less than 4500 mm², more preferably equal to or less than 3500 mm², and still more preferably equal to or less than 3000 mm². When the number of the low specific gravity members X1 is plural, the contact area Mc is the sum of contact areas of all the low specific gravity members X1.

[Material of Low Specific Gravity Member X1]

Preferable examples of the material of the low specific gravity member X1 include a polymer and a metal.

Examples of the polymer constituting the low specific gravity member X1 include an elastomer (including rubber) and a resin. Examples of the resin include a thermosetting resin and a thermoplastic resin. Examples of the thermosetting resin include a phenol resin, an epoxy resin, a melamine resin, a urea resin, an unsaturated polyester resin, an alkyd resin, polyurethane, and thermosetting polyimide. Examples of the thermoplastic resin include polyethylene, high-density polyethylene, medium-density polyethylene, low-density polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyvinyl acetate, polyurethane, polytetrafluoroethylene, an ABS resin (acrylonitrile butadiene styrene resin), an AS resin, an acrylic resin, nylon, polyacetal, polycarbonate, modified polyphenylene ether, polyethylene terephthalate, polybutylene terephthalate, cyclic polyolefin, polyphenylene sulfide, polytetrafluoroethylene, polysulfone, polyether sulfone, and polyether ether ketone. Fiber reinforced resins such as a carbon fiber reinforced resin may also be used.

The metal constituting the low specific gravity member X1 is preferably a metal having a relatively small specific gravity, such as a titanium-based alloy, a pure titanium, an aluminum-based alloy, and a magnesium-based alloy.

Examples of the titanium-based alloy constituting the low specific gravity member X1 include an a-titanium, an αβ-titanium, and a β-titanium. Examples of the α-titanium include Ti-5Al-2.5Sn and Ti-8Al-1V-1Mo. Examples of the αβ-titanium include Ti-6Al-4V, Ti-6A1-2Sn-4Zr-6Mo, Ti-4.5Al-3V-2Fe-2Mo and Ti-6Al-6V-2Sn. Examples of the β-titanium include Ti-15V-3Cr-3Sn-3Al, Ti-20V-4Al-1Sn, Ti-22V-4Al, Ti-15Mo-2.7Nb-3Al-0.2Si and Ti-16V-4Sn-3Al-3Nb.

As the pure titanium constituting the low specific gravity member X1, an industrial pure titanium is exemplified. As the industrial pure titanium, type 1 pure titanium, type 2 pure titanium, type 3 pure titanium, and type 4 pure titanium, which are defined by Japanese Industrial Standards, are exemplified.

Examples of the aluminum-based alloy constituting the low specific gravity member X1 include 2000 series, 3000 series, 4000 series, 5000 series, 6000 series, 7000 series, and 8000 series, which are indicated by four-digit numbers given as the international aluminum alloy designation. The 1000 series are pure aluminums. The 2000 series are Al—Cu-based alloy, and include duralumin (2017) and super duralumin (2024). The 3000 series are Al—Mn-based alloy. The 4000 series are Al—Si-based alloy. The 5000 series are Al—Mg-based alloy. The 6000 series are Al—Mg—Si-based alloy. The 7000 series are Al—Zn—Mg-based alloy and Al—Zn—Mg—Cu-based alloy, and are excellent in strength. The 7000 series include extra-super duralumin (7075) and 7N01.

Examples of the magnesium-based alloy constituting the low specific gravity member X1 include AZ31, AM60, AZ61, AZ80 and AZ91. These names are defined by ASTM.

More preferably, the material of the low specific gravity member X1 preferably has vibration absorbability. The vibration absorbability contributes to attaining a good feel at impact. In approach shots requiring a delicate sense, the good feel at impact contributes to improvement of controllability. In this respect, the material of the low specific gravity member X1 is preferably the polymer. In light of the vibration absorbability, the low specific gravity member X1 has a Young's modulus of preferably equal to or less than 5 GPa, more preferably equal to or less than 3 GPa, still more preferably equal to or less than 1 GPa, and yet still more preferably equal to or less than 0.5 GPa. It is also preferable that the Young's modulus is set to as low as 0.01 Gpa or greater but 0.1 Gpa or less. Examples of the material having such a low elastic modulus include rubber (elastic rubber).

[Specific Gravity of Low Specific Gravity Member X1]

In light of enhancing the weight re-distribution effect, the low specific gravity member X1 has a specific gravity of preferably equal to or less than 5, more preferably equal to or less than 4.6, and still more preferably equal to or less than 3. In light of durability of the low specific gravity member X1, the specific gravity of the low specific gravity member X1 is preferably equal to or greater than 1, and more preferably equal to or greater than 2.

[Material of High Specific Gravity Member Y1]

Preferable examples of the material of the high specific gravity member Y1 include a metal. A metal having a relatively great specific gravity is preferable. Examples of the metal having a high specific gravity include iron (specific gravity: 7.86), copper (specific gravity: 8.92), lead (specific gravity: 11.3), nickel (specific gravity: 8.85), zinc (specific gravity: 7.14), gold (specific gravity: 19.3), platinum (specific gravity: 21.4), osmium (specific gravity: 22.6), iridium (specific gravity: 22.4), tantalum (specific gravity: 16.7), silver (specific gravity: 10.49), brass (specific gravity: 8.5), and tungsten (specific gravity: 19.3). From the standpoint that lead is harmful and gold, silver, and the like are expensive, tungsten, copper, nickel and their alloys are preferable. In view of high specific gravity and processability, a tungsten-nickel alloy is particularly preferable.

[Specific Gravity of High Specific Gravity Member Y1]

In light of increasing the sweet spot height HS, the high specific gravity member Y1 has a specific gravity of preferably equal to or greater than 8, more preferably equal to or greater than 9, and still more preferably equal to or greater than 10. In view of availability of the material, the specific gravity of the high specific gravity member Y1 is preferably equal to or less than 20, and more preferably equal to or less than 19.

EXAMPLES

Hereinafter, the effects of the disclosure will be clarified by examples. However, the disclosure should not be interpreted in a limited way based on the description of examples.

Example

The same head as the head 2 was produced. The material of the head was soft iron. The head was produced by lost-wax precision casting. The specification of the head was as follows.

-   The real loft angle: 58° -   The sweet spot height HS: 20.6 mm -   The total volume VR of the back recessed parts Rb1: 4903.76 mm³ -   The interval DW of walls WL1: 10 mm (constant) -   The number N of the back recessed parts Rb1: 6 -   The thickness of the wall WL1: 2 mm (constant) -   The hosel length: 84 mm -   The minimum face thickness Tmin: 4.72 mm -   The area Ma of the minimum face thickness region: 806.65 mm² -   The area Mb of the thin region: 1189.25 mm² -   The face thickness Tf1 in the presence regions of the recessed part     front surfaces Rb2: 4.72 mm -   Wt2/Wt1: 1.849 -   Wt2/Wt3: 0.957 -   Wt1/Wt3: 0.517 -   The material of the low specific gravity member Xl: an epoxy resin

Comparative Example

A head according Comparative Example having the same weight (300 g) as in Example was obtained in the same manner as in Example except that the back recessed parts Rb1 were not provided and weight of the center region (the second portion H2) of the face was reduced. The specification of the head was as follows.

-   The real loft angle: 58° -   The sweet spot height HS: 18.2 mm -   The hosel length: 84 mm -   The minimum face thickness Tmin: 4.72 mm -   The area Ma of the minimum face thickness region: 1579.16 mm² -   The area Mb of the thin region: 1585.32 mm² -   Wt2/Wt1: 3.544 -   Wt2/Wt3: 0.811 -   Wt1/Wt3: 0.229

[Ball-Hitting Test]

A shaft and a grip were attached to each of the heads of Example and Comparative Example to obtain golf clubs having a club length of 35.25 inches. Five testers having a handicap of 10 or less carried out approach shots of 40 yards. Each of the testers hit a ball placed on a fairway five times with each of the clubs. The trade name “SRIXON Z-STAR XV3” manufactured by DUNLOP SPORTS CO., LTD. was used as the ball. The number NU of shots in which each tester felt that the hit ball had unintended initial speed or unintended trajectory was counted. Of 50 hits in total, the number NU of the shots was 2 for Example and 9 for Comparative Example.

From the results, the advantages of the embodiments are apparent. One of the reasons of the good results is considered to be the suppression of the high rebound property in the center portion.

The embodiments can be applied to iron type golf club heads.

The above description is merely for illustrative examples, and various modifications can be made without departing from the principles of the embodiments. 

What is claimed is:
 1. An iron type golf club head comprising a face surface formed by a face material, a back surface, and a sole surface extending between the face surface and the back surface, wherein the back surface includes a top side region and a sole side region positioned between the top side region and the sole surface, the sole side region includes a sole side inclination surface inclined to increase a face thickness toward a sole side, a plurality of back recessed parts formed on the sole side inclination surface, and at least one wall formed between the back recessed parts adjacent to each other, a low specific gravity member having a specific gravity lower than a specific gravity of the face material is disposed on at least one of the back recessed parts, the golf club head has a loft angle of equal to or greater than 42°, and the golf club head has a sweet spot height of equal to or greater than 18.5 mm.
 2. The iron type golf club head according to claim 1, wherein a high specific gravity member having a specific gravity higher than the specific gravity of the face material is disposed on the top side region.
 3. The iron type golf club head according to claim 1, wherein the number of the back recessed parts is equal to or greater than 5, and the number of the walls is equal to or greater than
 4. 4. The iron type golf club head according to claim 1, wherein the low specific gravity member is not disposed on at least one of the back recessed parts.
 5. The iron type golf club head according to claim 1, wherein the plurality of back recessed parts are arranged in a toe-heel direction.
 6. The iron type golf club head according to claim 1, wherein the plurality of back recessed parts include a first back recessed part positioned on a most heel side, a second back recessed part positioned on a most toe side, and a third back recessed part positioned between the first back recessed part and the second back recessed part.
 7. The iron type golf club head according to claim 1, wherein each of the back recessed parts forms a space between the face surface and the sole surface.
 8. The iron type golf club head according to claim 1, wherein an inner surface of each back recessed part has a recessed part front surface which is a surface opposite to the face surface.
 9. The iron type golf club head according to claim 1, wherein the wall extends in a direction perpendicular to the face surface.
 10. The iron type golf club head according to claim 2, wherein the high specific gravity member has a center of gravity positioned on an upper side with respect to a center of gravity of the head.
 11. The iron type golf club head according to claim 1, wherein a total volume of the back recessed parts is equal to or greater than 3500 mm³ but equal to or less than 6000 mm³.
 12. The iron type golf club head according to claim 1, wherein the plurality of walls are provided, and an interval of the walls is equal to or greater than 4 mm but equal to or less than 12 mm.
 13. The iron type golf club head according to claim 1, wherein the wall has a thickness of equal to or greater than 1 mm but equal to or less than 4 mm.
 14. The iron type golf club head according to claim 8, wherein the low specific gravity member is brought into contact with the recessed part front surface. 